1. Technical Field
The present invention relates to a tobacco filter having a ventilation effect. More specifically, the present invention relates to a tobacco filter which during smoking permits only external air to be guided through grooves around the filter core and prevents therethrough a substantial flow of tobacco smoke. This filter has small inhalation drag and the smoker can enjoy the feeling of ample smoke despite the smallness of the actual amount of smoke components being inhaled. In addition, the filter is capable of removing undesirable gaseous vapor components in the tobacco smoke.
2. Background Art
With the recent change in consumer's preferences toward "milder" tobacco, active R & D efforts are being made to develop tobacco smoke filters suitable for this purpose. The main aim of these efforts is directed to the development of filters capable of effective removal of components in the smoke particles such as tar and nicotine. Several methods have been proposed for attaining this object: one is by filling a single filter with an increased quantity of filter material, and another is by increasing the area of contact between the components in the smoke particles and the filter material during smoking by means of increasing the fineness of the filter material or by using a filter material with a profiled cross section. But the smoker is unable to enjoy smoking with the tobacco smoke filters made by these methods because they cause increased inhalation drag during smoking. A tobacco smoke filter free from this defect is described in U.S. Pat. No. 4,007,745. This filter is made of a thermally formed filter material having an embossed pattern. This filter is filled with an increased amount of filter material, but does not cause a corresponding increase in inhalation drag during smoking, and in addition, it is effective for removing components of the smoke particles. However, this filter is relatively ineffective in removing gaseous vapor components in tobacco smoke and does not present the smoker with the feeling of ample smoke inhalation.
Attempts are being made to develop materials for tobacco filters that are free from these defects. Japanese Patent Publication No. 31948/1981 (FR No. 2,373,975) discloses a tobacco smoke filter which, as shown in FIG. 1, comprises a filter core (1) wrapped with a corrugated tape (2) having a flat portion (3). An outermost layer of air-permeable paper (4) cooperates with the corrugated tape to define grooves through which external air that has penetrated the air-permeable paper is guided. This filter can be produced by a machine shown diagrammatically in FIG. 3. A sheet of paper (5) is fed through corrugation rolls (6) to form a sheet of corrugated paper having grooves (7) and flat portions (8) as shown in FIG. 2. The corrugated paper is wrapped around a filter tow (9), and then wrapped with a sheet of air-permeable paper (10). The resulting assembly is divided by a cutter (11) into a plurality of tobacco smoke filters each having the construction shown in FIG. 1. One defect with this method is that it is very difficult to cut the filter exactly at the very small flat portions (8) formed on the corrugated paper, and this difficulty must be eliminated before the method can be put to commercial use.